This invention relates to a worn lining wear indicator for a disc brake.
For safety, it is desirable to provide a device which warns the operator of a motor vehicle when the vehicle's brake linings have worn dangerously thin. Of course, when the brake lining has worn completely away, the brake becomes ineffective, and the rivet heads which are sometimes used to fasten the friction material on the backing plate or the backing plate itself come into contact with the brake disc or rotor, thereby damaging the rotor and requiring extremely expensive repairs. Many such brake lining warning devices have been proposed, but few have found commercial acceptance. In general, lining wear indicators have been of two types. Some lining indicators, such as that described in U.S. Pat. No. 3,556,258 and in U.S. Pat. No. 3,675,197, provide an electrical probe embedded in the friction lining which engages the brake disc or rotor after a predetermined amount of lining wear has occurred. Upon engagement of the probe with the grounded brake rotor, a warning device is actuated in the vehicle operator's compartment. Devices of this kind have the disadvantage of being relatively costly, and have the advantage of giving a precise indication of lining wear. The other types of brake lining wear indicators have been the so-called mechanical type, such as that disclosed in U.S. Pat. No. 3,368,519, which mounts a vibrating device on the friction element which, upon engagement with the rotor, makes a screeching noise. Devices of this type have the advantage of being relatively inexpensive, but suffer the disadvantage in that the screeching noise generated by this type of indicator is similar to many other brake noises, and therefore the warning may be overlooked by the vehicle operator.